Development of Repair Technologies for J-Groove Welds of Drain and Instrument Nozzle in Steam Generator

SG drain & instrument nozzles and their welds fabricated with alloy 600 and alloy 82/182 is susceptible to Primary Water Stress Corrosion Cracking (PWSCC). In Korea, the cracks due to PWSCC were discovered in the drain nozzle of Yongkwang units 3 & 4. Doosan has developed a system for steam generator to repair damaged drain nozzle & welds and to prevent further damage on the instrument nozzle & welds. The repair system consists of machining, welding equipment and installation tool for this equipment. The machining equipment is used to remove the nozzle and J-groove welds. The process is called mechanical machining and the main equipment is installed on steam generator’s outer wall. The welding equipment is designed for the machined J-groove welds and overlay. The auto welding equipment consists of welding head, controller, monitoring tool and Gas Tungsten Arc Welding (GTAW) power supply. Doosan has developed remote welding process using the monitoring tool. The installation tool consists of automatic installment tool for instrument nozzle and manual installment tool for drain nozzle. Doosan successfully completed a mockup test and field application for Yongkwang unit 3.